Motion capture essentially involves a detailed detection of movement by a person (actor) or some physical object, and an application of the detected movement to a virtual character or other computer-generated object. The detection can be done by way of affixing markers on the actor's body and then detecting, while the actor is moving, the markers' position optically or electromagnetically, to name two examples. The detected positions are encoded in one or more ways, and the resulting information is often referred to as motion capture data.
If the character that is driven by the motion-capture data represents a human with proportions identical to those of the actor, then the application of the actor's motion to the character usually does not raise any serious issues. That is, for almost any movement that one seeks to impart to the character, the actor can generate the necessary motion capture data by performing essentially the same movement on the motion capture stage. The same is true if the character does not represent a human but nevertheless has a body of approximately human configuration and proportions. For example, the character is a robotic character having a torso with two arms, two legs, and a head.
However, if the character's body configuration and/or proportions are instead different from those of the actor, then the application of the actor's motion to the character can run into one or more problems. For example, if the legs of the character are much longer than the actor's legs, then each step taken by the actor will translate into a much greater stride taken by the character. This can be undesirable, for example when two or more actors are being motion captured together, because the positions of the characters relative to each other will not be the same as those of the two actors. If one actor shakes the other's hand, for example, it is possible that the characters at this moment are too far apart so that their “hands” do not meet. As another example, if the actor is standing next to a table on the motion capture stage, the character may at the same time stand some distance away from the virtual table. Also, other factors can differ, such as the relative eyeline from one character to the other.